The mobile broadband era has arrived as the global deployment status of beyond 3G and 4G radio technologies suggests. Network densification along with universal resources reuse is expected to play a key role as an enabler for delivering most of the anticipated network capacity improvements. On the one hand, neither the expected additional spectrum allocation nor the forthcoming novel air-interface processing techniques will be sufficient for sustaining the anticipated exponentially-increasing mobile data traffic. On the other hand, enhanced ultra-dense infrastructure deployments are expected to provide remarkable capacity gains, regardless of the evolutionary or revolutionary approach followed towards 5G development. Recently, this ultra-dense network deployment (UDN) trend is gaining ground as it promises significant capacity improvements.
Ultra-dense networks (UDN) are wireless networks envisioned to provide ubiquitous mobile broadband with access-node densities considerably higher than the densest cellular networks of today, i.e. the distances between Access Node (AN) are from a few meters in indoor deployments up to around 50 m in outdoor deployment. A typical deployment for an UDN is in highly populated areas such as hot spots, office building, or downtown area at cities, where there are demands of high data rate service. The UDN may be designed to utilize an ultra frequency bands at 60 GHz with a wide bandwidth instead of low frequency bands with a clear bandwidth limit, in order to reach an even higher data rate. Therefore, a UDN is also referred as to a “Millimeter Wave (mmW) network.
Although network densification and universal resources reuse is a typical capacity increase strategy in the cellular paradigm, new challenges and issues arise. For example, heavy irregular infrastructure deployment of low-powered ANs leads to random topology networks, for which interference conditions characterization becomes harsh.
FIG. 1 schematically illustrates a scenario for inter-UDN interference. As shown in FIG. 1, two UDNs 110 and 120 are deployed in an office section and have coverage's overlapping with each other. The first UDN 110 comprises an AN 111 and an aggregation node (AGN) 112 which can be considered as a special AN and has a wired connection to a core network, and the second UDN 120 comprises ANs 121A and 121B, an AGN 122. For a subscriber to the first UDN 110, e.g., a terminal device (TD) 113A, a wireless link A is established between the TD 113A and the AN 111. Likewise, a subscriber to the second UDN 120, e.g., a terminal device (TD) 123B, a wireless link B is established between the TD 123B and the AN 121A. While these two subscriber move into the overlapping area, interference occurs between the wireless links A and B if the links share the same radio resource. Such interference may adversely affect traffic performance, especially when a significant number of the TDs are moving into the overlapping area.
Typically, an interference coordination process for radio resource is triggered while an interference power for one wireless link exceeds a pre-determined coordination threshold. It should be noted that coordination performance is susceptible to the threshold. FIG. 2 illustrates coordination performance as a function of threshold where curves “seed 1” and “seed 2” represent bit rates for two downlinks, which are managed by different UDNs overlapped with each other and share the same radio resource. From FIG. 2, it is observed the bit rates vary with the different threshold values and have the respective maximums. The curves suggest the complexity and importance of threshold selection, and therefore, a sophisticated solution for determining threshold becomes necessary for dealing with this issue.